Grinding segment and grinder stone

ABSTRACT

The invention relates to a grinding segment comprising a ceramic part manufactured of grinding ceramic material and provided with a fastening hole, through which the grinding segment is attached to a frame of a grinder stone by means of a fastening bolt. A fastening sleeve is arranged in the fastening hole, and the fastening bolt is supplied through the sleeve. The fastening sleeve is pressed against the frame of the grinder stone due to the fastening force. A space filled with bonding agent is formed between the ceramic part of the fastening sleeve to join them together. The invention further relates to a grinder stone comprising a cylindrical frame and grinding segments according to the invention.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates to a grinding segment comprising a ceramic partmanufactured of grinding ceramic material, at least one fastening holeformed in the ceramic part for fastening the grinding segment by meansof a fastening element to the outer surface of a frame of a grinderstone used in defibering of wood.

The invention further relates to a grinder stone for defibering wood,comprising a cylindrical frame, grinding segments made of grindingceramic material, arranged on the frame's outer circumference andfastened in place by means of a fastening element arranged through atleast one fastening hole formed in the segments, and a shaft, aroundwhich the grinder stone is arranged to be rotated during grinding.

2. Description of Related Art

Wood is typically ground into fibres by means of grinding machines,where logs are pressed against the surface of a rotating grinder stone.Water is simultaneously sprayed to purify and cool the grinder stone.The stone makes the wood fibre matrix vibrate, whereafter the woodfibres are released from the logs to provide a pulp suspension. Wood canbe ground under both a normal pressure and an overpressure.

The frame of the grinder stone is usually made of concrete. A grindingsurface consists of separate ceramic grinding segments attached to theframe. The prior art also teaches arrangements, where concrete framesare replaced with a steel drum. Steel is better able to withstand highgrinding forces generated during grinding than concrete. Also in a steeldrum the grinding segments are attached with suitable bolt mechanisms tothe outer circumference of the drum to form the grinding surface of thegrinder stone. Different segment fastening mechanisms are disclosed e.g.in FI 67,240. In this reference, a layer of rubber is disposed between agrinding segment and the steel drum to balance the loads between thesegment and the frame.

The prior art also teaches different fastening bolt mechanisms, whichcompensate for varying dimensions resulting from different thermalexpansion coefficients of the ceramic segment and the frame of thegrinder stone. However, such bolts are rather complicated and thereforealso expensive. Furthermore, it is possible to place semi-sphericalwashers between such bolts and the segment in order that the stressesresulting from the fastening will be distributed more evenly in thesegment and the segment will be able to withstand the fastening forces.Failure of a fastening bolt during use results in great damage and aninterruption of production. Another problem with the presentarrangements is that the fastening forces subject the ceramic segment tocompression stress, which can break the segment usually from below thewasher. It is thus necessary to restrict the fastening force, which insome cases can lead to insufficient fastening of the segment. Duringgrinding, such a loose segment can start vibrating and will be damaged.The ceramic materials used in grinding are highly wear-resistant andhard, yet brittle. However, in practice grinding segments cannot bemanufactured from more resistant ceramic materials, since the ceramicmaterial used in grinding of wood must be of a particular type andsufficiently porous to provide a desired grinding effect. Also, qualitycharacteristics set for mechanical pulp require use of the presentgrinding ceramic materials.

BRIEF SUMMARY OF THE INVENTION

An objective of the present invention is to provide a new and improvedgrinding segment and grinder stone for defibering wood.

A grinding segment according to the invention is characterized in that afastening sleeve is arranged in the fastening hole, that a layer ofbonding agent is formed between the fastening sleeve and the ceramicpart to join them together, and that the fastening element is arrangedto press the fastening sleeve to the frame of the grinder stone.

Further, a grinder stone according to the invention is characterized inthat each grinding segment comprises a fastening sleeve in connectionwith the fastening hole, that the fastening element is arranged to pressthe fastening sleeve to the frame of the stone, and that a layer ofbonding agent is formed between the fastening sleeve and the ceramicpart to join them together.

According to a basic idea of the invention, grinding segments placed onthe outer surface of the grinder stone comprise a ceramic partmanufactured of a suitable grinding ceramic material and provided withat least one fastening hole for a fastening bolt or some other similarfastening element. A fastening sleeve is arranged in each fasteninghole, so that between the sleeve and the fastening hole there remains aspace, where a layer of suitable bonding agent is formed. The fasteningsleeve and the ceramic part are connected by means of the layer ofbonding agent. The fastening bolts thus press the fastening sleeveagainst the frame of the grinder stone, wherefore the fastening force ofthe segment can be greater than previously, and firmer fastening isprovided. Furthermore, since the fastening element, the fastening sleeveand the frame of the grinder stone are made of the same material,thermal expansion is under control. Also, the layer of bonding agentbetween the sleeve and the ceramic part balances the loads.

Furthermore, according to a basic idea of a preferred embodiment of theinvention, a predetermined proportion of the ceramic part of thegrinding segment, beginning from the bottom of the segment towards thegrinding surface, is impregnated with bonding agent, such as suitableplastic. This avoids the occurrence of breakage and makes the segmentmore capable of withstanding loading. Also, the joint between thefastening sleeve and the ceramic material will be more secure.

According to a basic idea of another preferred embodiment of theinvention, side surfaces of the grinding segment, which are transverseto the bottom of the segment and possibly also to the grinding surface,are provided with damping layers made of bonding agent. The bottom ofthe segment thus comprises an intermediate layer in the area of theceramic part to balance loads and possible unevenness of the fasteningsurface. When the grinder stone is being used, the side layers in theside surfaces of adjacent grinding segments are positioned tightlyagainst one another, and a point load subjected on an individual segmentis therefore also distributed onto adjacent segments.

It should be mentioned that in the present application the term ‘grinderstone’ refers to the stone frame and the assembly of the grindingsegments and fastening means arranged thereto.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING(S)

The invention will be described in more detail in the accompanyingdrawings, in which

FIG. 1 shows schematically a grinding apparatus, where a grindingsegment according to the invention can be used,

FIG. 2 is a schematic end view of a grinder stone according to theinvention, and

FIG. 3 is a schematic side view of a part of the grinder stone accordingto the invention,

FIGS. 4 and 5 are schematic sectional views of grinding segmentsaccording to the invention and the fastening thereof,

FIG. 6 shows schematically placement of segments according to theinvention on the outer circumference of a frame of the grinder stone,

FIGS. 7 and 8 are schematic sectional side views of embodiments of theinvention,

FIG. 9 a is a schematic top view of a part of a grinder stone accordingto the invention, and FIG. 9 b shows schematically a grinding segmentaccording to FIG. 9 a viewed from direction A, and

FIG. 10 a is a schematic top view of a grinding segment according to theinvention, and FIGS. 10 b and 10 c show embodiments of the grindingsegment viewed from direction B.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 shows a grinding apparatus for detaching fibres from logs 1 orsome other similar wood material by means of a rotating cylindricalgrinder stone 2. The logs 1 are pressed by feeder means, such as feedcylinders 3, from a feed chamber 4 against the outer surface of thegrinder stone 2. Water is simultaneously supplied from nozzles 6 to agrinding chamber 5. The fibre that has been released from the logsaccumulates with the sprayed water in a grinder pit 7 at the bottom ofthe grinding chamber and is conducted therefrom to subsequent processingsteps. The grinding apparatus is considered fully known to a personskilled in the art, wherefore the structure and operation thereof do nothave to be described in more detail herein.

FIG. 2 shows, in a simplified manner, a grinder stone 2, which rotatesaround a shaft 8. The grinder stone comprises a preferably metalcylindrical frame 9, the outer circumference of which is provided withadjacent grinding segments 10 typically made of ceramic, a suitableceramic mixture or some other corresponding material. The segmentsconstitute a grinding surface 30 of the grinder stone that processes thewood. The fastening of the grinding segments to the frame will bedescribed in more detail in FIGS. 4 and 5 below. FIG. 3 is a side viewof a part of the grinder stone.

FIG. 4 shows a cross-sectional view of the structure of the grindingsegment 10. The segment comprises a ceramic part 11 manufactured ofceramic or some other material that is suitable for grinding. The shapeand size of the segment can be selected separately in each case. Thebottom of the segment is typically curved and corresponds to the shapeof the outer circumference of the stone frame. The outer surface of thesegment is also curved, as shown in FIG. 2, for example. Fastening holes12 extend through the ceramic part 11 for fastening bolts 13 or someother similar fastening means that are screwed onto the frame 9 of thegrinder stone. Three or more fastening bolts are preferably used foreach segment. According to the basic idea of the invention, the segmentcomprises fastening sleeves 14, preferably made of steel or the like,which coincide with the fastening holes. A fastening bolt goes through afastening sleeve. For the sake of clarity, the figure shows thefastening sleeve with a rather thick wall structure. The fastening forceprovided by the fastening bolt does not directly cause compressionstress in the ceramic part, but the fastening bolt tightens thefastening sleeve against the frame of the grinder stone. Since thefastening bolt affects directly the fastening sleeve of steel, it is nolonger necessary to use such conventional structures as semi-sphericalwashers for balancing stresses, but a standard locking washer 15, suchas a spring washer or the like, can be disposed between the sleeve andthe bolt. Due to the fastening sleeve, the tightening force does nothave to be restricted according to the compression resistance of theceramic material, but such a high fastening force can be selected thatthe segment is guaranteed to stay in place. Another advantage of thearrangement is that the thermal expansion coefficients of the fasteningbolt, the fastening sleeve and the frame of the grinder stone aresubstantially equal since the components are made of the same material,which is typically steel. Therefore thermal expansion resulting fromheating of the grinder stone is always under control, and there is noneed for complicated and expensive special bolts to compensate forthermal expansion.

As shown further in FIG. 4, a space filled with bonding agent isprovided between the fastening sleeve 14 and the ceramic part 11. Thebonding agent can be for example cast resin, such as vinylester-polyurethane (VEUH), vinyl ester (VE), polyurethane (PU), andepoxy resins. Other possible bonding agents include natural rubber,polystyrene (PS), poly-phenylenesulphide (PPS), polyamide (PA) and othersuitable plastic materials. Moreover, the bonding agent can bereinforced with fibre or it can contain filler. The fibre reinforcementcan consist of such fibre material as a glass fibre mat or a glass fibremesh, staple glass fibre, milled glass fibre, kevlar, carbon fibre orsome other suitable fibre material. The filler can be aluminium oxide,silica sand, kaolin, talc or some other suitable filler. In some cases,different cements and metallic soldering materials can also be used asbonding agent. The fastening force is transmitted from the fasteningsleeve to the ceramic part via the aforementioned layer 16 of bondingagent. The layer has a thickness of 0.1 to 3 mm, preferably 0.3 to 1 mm.The layer of bonding agent is also able to compensate for deviationsbetween the ceramic part 11 and the fastening sleeve 14 resulting fromdifferent thermal expansion coefficients of the materials. Furthermore,the bottom of the ceramic part is preferably provided with a layer ofcorresponding bonding agent, which forms a damping intermediate layer 20between the segment and the frame. The intermediate layer dampspercussive loads possibly directed at the segment during the grinding ofwood, thus preventing segment breakage. It also prevents vibration inthe segment. Furthermore, the intermediate layer 20 balances any slightunevenness that possibly occurs between the joint surfaces of thesegment and the frame of the grinder stone, thus improving thefastening. Due to the intermediate layer, the segment bottom and thefastening surface formed in the frame of the grinder stone do not haveto be perfectly finished during the manufacture, which reduces the costsof manufacture. The intermediate layer has a thickness of preferably 1to 3 mm. On the other hand, the intermediate layer is not necessary.

The segment shown in FIG. 5 mainly corresponds to the segment shown inFIG. 4. However, in FIG. 5 a proportion of the bottom section 17 of thesegment is impregnated with plastic bonding agent beginning from thesegment's bottom towards a grinding surface 30 of the segment. Theimpregnated bottom section 17 prevents the formation of ruptures in thesegments and improves the joint between the ceramic part and thefastening sleeve. The impregnation is preferably carried out from thelower surface of the segment approximately to the level of the upper endof the fastening sleeves, but it can also be performed closer to theupper surface of the segment. For the sake of illustration, a brokenline 18 in the figure shows different possible locations of theinterface between the impregnated bottom section 17 and the surfacesection 19. Between the grinding surface 30 and the impregnated part 17of the segment there is a nonimpregnated section with good grindingproperties. The grinding section of the grinder stone can be sharpenedas the need arises, so that when the segment is finally replaced as aresult of normal wearing, the grinding section has been used all the wayto the impregnated section. Furthermore, the segment side surfaces arepreferably provided with side layers 21 formed of bonding agent, whichact as damping parts between adjacent segments. The side layers 21 havea thickness of preferably 1 to 3 mm and they extend preferablysubstantially to the level of the impregnated bottom section 17 of thesegment. The side layers are preferably arranged in all the sides of thesegment that are transverse to the grinding surface. If required, someor all of the side layers can be eliminated. Furthermore, the fasteningsleeves 14 of the segment according to FIG. 5 differ from thecylindrical sleeves shown in FIG. 4. In FIG. 5, the outer surfaces ofthe fastening sleeves comprise one or more protrusions 28. The sleeve'souter surface is preferably wavelike, and the wave's cross-section issimilar to a sine wave. The wave shape can also be similar to a squarewave, a saw-tooth wave, etc. The protrusion can also resemble a thread.Correspondingly, the circumference of the fastening hole formed in theceramic part can be provided with one or more protrusions in the sectioncorresponding to the level of the fastening sleeve, the protrusionspreferably corresponding to those in the sleeve. The shapes of theprotrusions in the ceramic part and in the fastening sleeve can alsodiffer from one another, if necessary, and protrusions can only beprovided in one element and not in the other. The purpose of theprotrusions is to improve the joint between the ceramic part and thefastening sleeve, and the shape of the protrusions can be used to adjustthe behaviour of the segments under stress.

The intermediate layer 20 and the side layers 21 shown in FIG. 5 canalso be components made of suitable bonding agent and separate from theceramic part 11. Furthermore, the bonding agent used in the intermediatelayer 20, the side layers 21 and the space between the fastening sleeve14 and the ceramic part 11 can be reinforced with glass fibre or thelike.

FIG. 6 shows a preferred arrangement for fastening segments. The outercircumference of the frame 9 of the grinder stone is provided withplanar sections 22 a to 22 c, parallel to the shaft of the grinderstone, for the segments. The planar sections are also provided withfastening holes 23, so that the segments 10 can be attached to the frameof the grinder stone by means of fastening bolts 13. As shown in thefigure, each segment is provided with three fastening bolts to ensurestable fastening that prevents swaying. Viewed in the direction of theradius of the grinder stone, the segments 9 shown in the figure comprisea base 24, two sections 25 a and 25 b that are perpendicular to thebase, and a triangular apex 26 extending from the sections. Such sectorscan be arranged in the planar sections of the frame in alternatingdirections, such that the bases 24 are parallel to the frame shaft or tothe edge of the planar section, and the apices of adjacent segments thuspoint in opposite directions. In such a manner the segments can bepositioned tightly against one another to constitute a grinding surface.The segments of the entire grinder stone can thus be of the same shape,excluding end segments 27 to be placed at the end of the grinder stone.When damaged or worn-out segments are being replaced, it is notnecessary to remove the grinder stone from the grinding apparatus, butsegments can be detached and attached while the stone is in place, e.g.via an opening provided in the grinding apparatus for sharpening thegrinder stone.

FIG. 7 shows an arrangement, where a transverse support element 40 isarranged between the upper end of the fastening sleeve 14 and thefastening bolt 13 to secure the fastening of the segment. The segment isprovided with an opening, transverse to the fastening hole 12, forreceiving the support element 40. Bonding agent 16 is applied betweenthe support element and the transverse opening. The support element ispreferably rectangular, but the shape can be selected suitably in eachcase.

FIG. 8 shows a conical fastening sleeve 14, which is arranged with thegreater sleeve diameter on the side of the segment's upper surface. Theconical fastening sleeve ensures firm fastening of the segment. Thefastening sleeve 14 can also be a separate piece, which is precoatedwith a required layer 16 of bonding agent and thereafter arranged in afastening hole 12 in the ceramic part 11. When the fastening element 13is being tightened, the layer 16 of bonding agent in the fasteningsleeve is pressed against the ceramic part 11 to join the part to thefastening sleeve. On the other hand, the layer of bonding agent betweenthe fastening sleeve and the ceramic part can be a preformed separatepiece.

The grinder stone 2 shown in FIG. 9 a comprises rectangular grindingsegments 10, which are attached to the stone's outer surface with twofastening bolts or a corresponding fastening element. As shown in FIG. 9b, the grinding segments 10 have a curved bottom surface, so that thesegment rests against the curved outer surface of the frame 9 of thegrinder stone.

FIGS. 10 a to 10 c show grinding segments 10, where the bottoms compriseone or more protrusions 50 or grooves 51. The outer surface of the frame9 of the grinder stone is also provided with sections that fit in theaforementioned protrusions or grooves, so that shear forces producedduring the use of the grinder stone can be transmitted from the grindingsegment to the stone frame. Such fastening of the grinding segment isfirm, and only one tightening bolt per segment may be sufficient. In thearrangements shown in FIGS. 9 a to 10 c, each fastening hole is providedwith a fastening sleeve according to the invention.

The drawings and the related description are only intended to illustratethe inventive idea. The details of the invention can vary within thescope of the claims. It is thus clear that even if the segmentsadvantageously have a similar shape as shown in FIG. 6, the fasteningarrangement according to the invention can also be applied in connectionwith segments of other shapes. The bonding agent to be used between thefastening sleeve and the ceramic part, the bonding agent thatimpregnates the segment, the bonding agent in the bottom of the segment,and the bonding agents in the side layers of the segment can bedifferent in some cases, although with respect to the manufacturingtechnique it is advantageous to mould all the aforementioned layers ofbonding agent simultaneously. Furthermore, the intermediate layer can bemade to extend beyond the fastening sleeve at the bottom of the segment,so that when the segment is tightened in place, the intermediate layeris compressed to some extent so as to produce a predetermined initialtension, which prevents occurrence of vibrations. Also, even though theinvention is described in the figures in connection with a grinder stoneof a steel frame, the invention can also be applied in grinder stoneswith a frame of concrete.

1. A grinding segment comprising a ceramic part manufactured of grindingceramic material, at least one fastening hole formed in the ceramic partfor fastening the grinding segment by means of a fastening element tothe outer surface frame of a grinder stone used in defibering of wood,fastening sleeve arranged in the fastening hole, and a layer of bondingagent formed between the fastening sleeve and the ceramic part to jointhem together, the fastening element being arranged to press thefastening sleeve to the frame of the grinder stone, wherein apredetermined proportion of the ceramic part of the grinding segment isimpregnated with bonding agent beginning from the bottom of the segmenttowards the grinding surface thereof.
 2. A grinding segment according toclaim 1, wherein the outer surface of the fastening sleeve is providedwith protrusions.
 3. A grinding segment according to claim 1, whereinthe inner surface of the fastening hole formed in the ceramic part isprovided with protrusions over a section corresponding to the fasteningsleeve.
 4. A grinding segment according to claim 1, wherein the bottomof the grinding segment in the area of the ceramic part is provided withan intermediate layer of bonding agent arranged to remain between theframe of the grinder stone and the ceramic part of the grinding segmentwhen the segment is installed in place.
 5. A grinding segment accordingto claim 1, wherein at least some of the sides of the grinding segment,transverse to a grinding surface are provided with side layers ofbonding agent, which are arranged to be disposed towards adjacentgrinding segments when the segment is in place in the grinder stone. 6.A grinding segment according to claim 1, wherein a proportion of thegrinding segment that corresponds substantially to the fastening sleevesis impregnated with bonding agent beginning from the bottom of thesegment towards the grinding surface.
 7. A grinding segment according toclaim 1, wherein the bonding agent is reinforced with fibre.
 8. Agrinding segment according to claim 1, wherein a proportion of thegrinding segment about the at least one fastening hole is impregnatedwith bonding agent beginning from the bottom of the segment towards thegrinding surface thereof.
 9. A grinder stone for defibering wood,comprising a cylindrical frame, grinding segments made of grindingceramic material and arranged on the frame's outer circumference, eachgrinding segment being fastened to the frame by a fastening elementextending through a fastening hole defined by the respective grindingsegment, and a shaft around which the grinder stone is arranged to berotated during grinding, each grinding segment comprising a fasteningsleeve disposed within the fastening hole, wherein the fastening elementis configured to secure the fastening sleeve to the frame of the grinderstone, and wherein a bonding agent is inserted between the fasteningsleeve and a surface of the grinding segment defining the fastening holeso as to secure the fastening sleeve within the fastening hole.
 10. Agrinder stone according to claim 9, wherein the outer circumference ofthe frame of the grinder stone is provided with planar sections,parallel to the shaft of the stone, for fastening the grinding segmentsthereto.
 11. A grinder stone according to claim 9, wherein each grindingsegment includes an engagement surface for engaging the frame, andwherein the fastening sleeve extends from the engagement surface andinto the grinding segment such that fastening element exerts a securingforce for securing the grinding segment to the frame through thefastening sleeve.